1. Field of the Invention.
The present invention relates to grounding bushings that are used with conduits in electrical panels and which include lugs for receiving a grounding conductor which must be secured to the bushing.
2. Description of the Prior Art.
Various grounding bushings have been advanced and used. These grounding bushings include various coupling lugs for ground wires of different configurations, but the problem of easy and secure attachment of a grounding bushing for installing the grounding lug and attaching the grounding conductor when the bushing is in place on a conduit on the inside of an electrical panel or box remains.
Grounding bushings on the market cannot always be turned on or threaded onto the conduit tightly and still use the provided grounding lug. Some types of bushings have a protruding grounding lug on the outside and that makes it impossible to turn the bushing onto the threads at all, particularly when the conduit is placed near a corner of the electrical panel or box. If the lug is removed from the bushing before turning it on, many times it cannot be replaced again after the bushing has been fully tightened on the conduit because the position for attaching the lug on the bushing may be closely adjacent to a side wall of the box, or otherwise inaccessible in the box. When the bushing is turned on tight with the lug attached, the lug always seems to be facing in such a direction that the grounding conductor cannot be placed into the lug, or where the lug cannot be drawn down tight onto the conductor. Usually the reason the lug cannot be drawn down tight is that the screwdriver that is necessary for tightening the screw against the grounding conductor cannot be placed in line or in axis with the screw. If the bushing is backed off or unthreaded to a point where the lug is accessible, grounding that is supposed to be accomplished through the set screw that ties the bushing into place is questionable. Many times the set screws are so small the electrician does not have a small enough screwdriver to tighten down the set screw securely, if he is able to get at it at all.
Additionally, many of the grounding lugs are of the "tunnel" type where the electrician must thread the grounding conductor through a hole in the lug, which consumes unnecessary time and often kinks and damages the grounding conductor itself. After the grounding conductor has finally been secured into the tunnel lug, the lug is usually loosened up on the bushing. With the grounding conductor in place the lug cannot be retightened onto the bushing because in most cases the grounding conductor passes directly in front of the head of the screws which hold the lug onto the grounding bushing.
While some of the grounding devices have a "lay in lug" the inability to move the lug to different positions on the bushing easily forces the electrician to attach the grounding conductor wherever the lug happens to rest when the bushing is turned on tight. These problems and others described in the following prior art are overcome with the present device.
U. S. Pat. No. 4,189,198 shows a conduit ground wire coupling that has a grounding lug attachable thereto, and which has a multiple number of positions at which the grounding lug can be attached. However, the screws for attaching the grounding lug are positioned so that when the grounding lug is to be installed, the short stubby screw cannot be reached easily with a screwdriver for fastening. Also, because the grounding lug itself will shield the screw that holds it in place from view, it is difficult to keep the screwdriver in place.
U.S. Pat. No. 4,210,374 also shows a bushing including an integral electrical clamp for a ground wire. Integral clamps make it almost impossible to rotate the bushing in place on threaded conduit connections, and while U.S. Pat. No. 4,210,374 shows a slip-on bushing, this still involves the need for access from two distinct angles. Further there is a need for fastening the bushing and the grounding conductor which is many times inaccessible as well.
U.S. Pat. No. 4,159,859 shows a cradle-type ground lug which is attached in place with a set screw, but the ground lug is shown in an awkward position for installing any type of a ground conductor. Thus using the bushing is extremely difficult, even though the bushing itself in this particular patent shows a plurality of tapped holes, one on each of the conventional, flat outer surface bosses on the outside periphery of the grounding bushing.
A patent that shows a grounding bushing that has an inclined, forwardly facing surface on a boss on its periphery is U.S. Pat. No. 2,974,185. However, use of this type of a bushing is limited to number 10 American Wire Gauge or smaller. Using this type of a bushing in communication with a lug that will receive a grounding conductor simply and easily is not shown or suggested. Accessibility of a boss as well as turning it on remain problems when the device is installed in an electrical box.
A cradle-type ground lug for a conduit is also shown in U.S. Pat. No. 3,967,872, and this particular ground lug spans two bosses on the outside of a grounding bushing, but is only capable of being installed in one location on the bushing, and thus installation at many times will be difficult and further the grounding lug connections are not very secure. The set screw shown at 41 is not accessible after the grounding conductor is in place. The grounding bushing requires access at two points 90.degree. apart.
A square throat cable connector having inclined bosses that are drilled and tapped to receive clips are shown in U. S. Pat. No. 3,006,981. This cable connector does not have the ruggedness and strength required for a grounding lug. Commercially available grounding bushings conform generally to the teaching of this prior art.
In all of the prior art, the difficulties of accessibility, ease of installation and obtaining proper grounding connections remain.